explicit barrier( std::ptrdiff_t num_threads );
barrier( const barrier & ) = delete;
1) Constructs a
num_threadsparticipating threads. The set of participating threads is the first
num_threadsthreads to arrive at the synchronization point.
2) Copy constructor is deleted;
barrieris not copyable.
|num_threads||-||the number of participating threads for the barrier; must be non-negative|
num_threads is zero, the set of participating threads is empty, and barrier can only be destroyed.